In the field of medical imaging systems it is generally known to combine different images of a patient acquired by different medical analysis systems in order to improve the diagnostic possibilities. In particular, ultrasound systems are known which combine ultrasound images and pre-operative image data of a patient derived from a different imaging system. The ultrasound system is provided with a probe position tracking system to determine the position of the ultrasound probe at the patient's body to correlate the corresponding ultrasound images with the pre-operative volume analysis data. The positioning system enables a continuous spatial alignment of the pre-operative data and the live ultrasound data.
The position tracking systems rely on a calibration based e.g. on artificial markers which can be identified in the pre-operative and the ultrasound data and which can be correlated to each other so that the alignment of the data can be determined. The position tracking system may also comprise an electromagnetic tracking system which determines an offset between a sensor coordinate system and an ultrasound coordinate system. Such a probe positioning system is e.g. known from WO 2012/117381 A1.
The probe positioning systems usually have a high accuracy in the vicinity of the markers, however, the accuracy is reduced if the probe is moved away from the markers. Further, if a misalignment between the pre-operative data and the ultrasound data occurs, a manual readjustment is necessary, which is time-consuming and requires detailed expert knowledge.